Improve list diffing/patching performance

[JaggerJo]

FuncUI currently implements super simple list diffing that works just fine in most cases.

There are cases where a list contains complex or a lot of different items this can be problematic. Especially when items are inserted at index 1 - because this currently will result in rebuilding all items.

Implementing a 2nd list diffing strategy that utilises keys to reduce the required patch work could speed up list diffing by a lot. (here is how react does it)

Adding a Key to Avalonia Controls is easily possible using AttachedProperties. (We actually implicitly attache properties to controls for internal subscription handling - IIRC)

StackPanel.children [
    TextBlock.create [
        TextBlock.key "item 1"
        TextBlock.text "item 1"
        ...
    ]
    ...
]